How the Invasion Zone Can Contribute to the Estimation of Petrophysical Properties From Log Inversion at Well Scale?
- Thibaud Vandamme (MODIS) | Emmanuel Caroli (Total) | Serge Gratton (ENSEEIHT)
- Document ID
- Society of Petrophysicists and Well-Log Analysts
- Publication Date
- April 2019
- Document Type
- Journal Paper
- 306 - 325
- 2019. Society of Petrophysicists & Well Log Analysts
- 1 in the last 30 days
- 90 since 2007
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In a conventional formation evaluation process, the mud-filtrate invasion in the near-wellbore region is considered a bias that requires a well-log correction before any petrophysical evaluation. The developments presented in this paper show that the invasion zone is a valuable source of information to estimate dynamic properties that generally come only from core measurements, such as permeability, relative permeabilities, capillary pressure curves and formation factor.
In this approach, the invasion process is not simulated in itself, as it would lead to a very unstable inverse problem within the time frame of the logging. On the contrary, it considers the fluids in the invaded domain as radially equilibrated and solves the fluid distribution governed at first-order by capillary pressures. Due to the multimodality of the inverse problem and the uncertainties related to the mud-filtrate parameters, the invasion zone is jointly inverted with the vertical capillary equilibrium at field-scale describing the vertical water saturation profile in the reservoir for each facies. The following workflow is then used: First, the invasion is solved in the water intervals while inverting the resistivity logs. The resolved parameters are the local volume of filtrate, pseudopermeabilities and cementation factors at each depth. At the end of this step, we get an insight of the number of petrofacies and the correlation between permeabilities and porosities inside each of these. Second, the inversion in itself is carried out in the hydrocarbon zone by exploiting the grouping from the first step. The vertical capillary equilibrium is added and updates permeabilities (absolute and relative) as well as capillary pressure models for each facies.
In the context of this paper, we present a vertical well and consider a radial oil-based mud invasion. We also assume isotropic petrophysical parameters. The final results are compared to all available sources of data, such as NMR, WFT and cores for permeabilities, formation factor and capillary pressure curves.
The ultimate added value of such an approach is to bridge static and dynamic petrophysical parameters from a single source of data: logs. It provides a reliable first guess of petrophysical and reservoir parameters at an early stage of the well evaluation. It also ensures an overall consistency of the formation model for the whole range of facies and fluid configurations. The technique can even help in the formation heterogeneity and petrophysical upscaling when run in a multiwell configuration.
|File Size||11 MB||Number of Pages||20|